C-style for loop in Bash Scripting - Mini Project: Build & Apply

Using C-style for loop in Bash scripting

📖 Scenario: You are managing a small inventory system using a Bash script. You want to count from 1 to 5 to simulate checking five items in stock.

🎯 Goal: Build a Bash script that uses a C-style for loop to count from 1 to 5 and print each number.

📋 What You'll Learn

Create a variable called start and set it to 1

Create a variable called end and set it to 5

Use a C-style for loop with i starting from start to end

Print the value of i inside the loop

💡 Why This Matters

🌍 Real World

Counting or iterating a fixed number of times is common in automation scripts, like processing files or checking system status.

💼 Career

Knowing how to write loops in Bash helps in system administration, DevOps, and automation roles where scripts manage repetitive tasks.

1

Set up start and end variables

Create a variable called start and set it to 1. Create another variable called end and set it to 5.

Bash Scripting

# Your code here

Hint

Use start=1 and end=5 to create the variables.

2

Write the C-style for loop

Write a C-style for loop using i starting from start to end. Use the syntax for (( i=start; i<=end; i++ )).

Bash Scripting

start=1
end=5
# Your code here

Hint

Use for (( i=start; i<=end; i++ )) and echo $i inside the loop.

3

Add the loop body to print numbers

Inside the for loop, write echo $i to print the current value of i.

Bash Scripting

start=1
end=5
for (( i=start; i<=end; i++ ))
do
    # Your code here
done

Hint

Use echo $i to print the number inside the loop.

4

Run the script and display output

Run the script and print the numbers from 1 to 5, each on its own line.

Bash Scripting

start=1
end=5
for (( i=start; i<=end; i++ ))
do
    echo $i
done
# Run the script to see output

Hint

Run the script using bash script.sh or execute it directly.

Practice

1. What does the following C-style for loop do in bash?
for ((i=1; i<=3; i++)); do echo $i; done

easy

A. Prints numbers 1, 2, and 3 each on a new line

B. Prints numbers 0, 1, and 2 each on a new line

C. Prints numbers 1, 2, 3, and 4 each on a new line

D. Causes a syntax error

Solution

1. Step 1: Understand the loop initialization and condition

   The loop starts with i=1 and runs while i is less than or equal to 3.

2. Step 2: Analyze the increment and output

   Each iteration prints the current value of i, then increases i by 1 until i becomes 4 and stops.

3. Final Answer:

   Prints numbers 1, 2, and 3 each on a new line -> Option A

4. Quick Check:

   Loop from 1 to 3 prints 1, 2, 3 [OK]

Hint: Check start, end, and increment values carefully [OK]

Common Mistakes:

• Starting loop at 0 instead of 1
• Confusing <= with < in condition
• Forgetting to increment i

2. Which of the following is the correct syntax for a C-style for loop in bash?

easy

A. for (i=0; i<5; i++) do echo $i; done

B. for ((i=0; i<5; i++)); do echo $i; done

C. for [i=0; i<5; i++] do echo $i; done

D. for {i=0; i<5; i++} do echo $i; done

Solution

1. Step 1: Identify correct C-style for loop syntax in bash

   Bash requires double parentheses (( )) around the loop control with semicolons separating init, condition, and increment.

2. Step 2: Check each option

   for ((i=0; i<5; i++)); do echo $i; done uses double parentheses and semicolons correctly; others use incorrect brackets or missing parentheses.

3. Final Answer:

   for ((i=0; i<5; i++)); do echo $i; done -> Option B

4. Quick Check:

   Double parentheses and semicolons = correct syntax [OK]

Hint: Look for double parentheses and semicolons inside [OK]

Common Mistakes:

• Using single parentheses instead of double
• Using square or curly brackets
• Missing semicolons between parts

3. What is the output of this bash script?

for ((i=2; i<=6; i+=2)); do echo $i; done

medium

A. 2 3 4 5 6

B. Syntax error

C. 2 4 6 8

D. 2 4 6

Solution

1. Step 1: Understand loop initialization and increment

   The loop starts at i=2, runs while i is less than or equal to 6, and increments i by 2 each time.

2. Step 2: List values printed

   Values printed are 2, then 4, then 6. After 6, i becomes 8 which breaks the condition.

3. Final Answer:

   2 4 6 -> Option D

4. Quick Check:

   Increment by 2 from 2 to 6 prints 2,4,6 [OK]

Hint: Check increment step and loop condition carefully [OK]

Common Mistakes:

• Assuming increment is 1 by default
• Including numbers beyond the condition
• Confusing <= with <

4. Identify the error in this bash C-style for loop:

for ((i=0; i<5 i++)); do echo $i; done

medium

A. Missing semicolon between condition and increment

B. Using single parentheses instead of double

C. Incorrect variable name

D. Missing do keyword

Solution

1. Step 1: Check loop syntax parts

   The loop control must have three parts separated by semicolons: initialization, condition, and increment.

2. Step 2: Locate missing semicolon

   Between 'i<5' and 'i++' there is no semicolon, causing a syntax error.

3. Final Answer:

   Missing semicolon between condition and increment -> Option A

4. Quick Check:

   Semicolons separate parts in C-style for loops [OK]

Hint: Check for three semicolon-separated parts inside (( )) [OK]

Common Mistakes:

• Omitting semicolons between parts
• Using single parentheses
• Forgetting do keyword

5. You want to print all odd numbers from 1 to 9 using a C-style for loop in bash. Which script achieves this?

hard

A. for ((i=1; i<10; i++)); do if (( i % 2 == 0 )); then echo $i; fi; done

B. for ((i=0; i<10; i++)); do if (( i % 2 == 0 )); then echo $i; fi; done

C. for ((i=1; i<=9; i+=2)); do echo $i; done

D. All of the above

Solution

1. Step 1: Analyze for ((i=1; i<=9; i+=2)); do echo $i; done

   for ((i=1; i<=9; i+=2)); do echo $i; done starts at 1, increments by 2, prints 1,3,5,7,9 directly.

2. Step 2: Analyze options B and C

   Both loop with i++ and check if (( i % 2 == 0 )), which selects even numbers: B prints 0,2,4,6,8; C prints 2,4,6,8.

3. Final Answer:

   for ((i=1; i<=9; i+=2)); do echo $i; done -> Option C

4. Quick Check:

   Increment by 2 from 1 to <=9 prints odds 1-9 [OK]

Hint: Use increments or modulo checks to filter odd numbers [OK]

Common Mistakes:

• Using wrong increment step
• Starting from 0 without filtering
• Forgetting to check odd condition